Also in this chapter:

1.3 A Multi-Dimensional Challenge

In assessing these issues we are confronted with a series of highly complex issues, which result from both scientific and political factors.

In Chapter 2, we focus on the likelihood of various emission pathways staying within temperature limits. For these pathways we identify the period in which emissions peak, the level of emissions in 2020, and the corresponding emission reduction rates after 2020. Results include emission pathways from integrated assessment models (IAM) and carbon cycle and climate models. Also discussed are current views about the feasibility of emission reductions and negative emissions, as well as factors determining long-term temperature, including cumulative emissions.

Chapter 3 reviews estimates of global emission levels in 2020 based on country emission pledges. Among the factors influencing these estimates are whether pledges are independent of, or conditional on, other countries’ actions, financing or technological support. For industrialized countries, key factors include: the accounting procedures for emissions or uptake of carbon from land use, land-use change and forestry (LULUCF); the potential for international climate finance, as agreed in the Copenhagen Accord to enable further emission reductions; the carry-over of emission reduction units from the first commitment period of the Kyoto Protocol (2008-2012); and the potential double counting of offsets with emission reductions from non-Annex I countries’ actions. Emission estimates are also influenced by the uncertainty of base year emissions and by assumptions needed for filling in sectoral or other gaps in the emission estimates of various groups.

The pledges of industrialized countries are fairly easy to convert into emission estimates because they are usually related to historic emissions. However, more assumptions are needed to make this conversion for developing countries because their pledges have usually been pegged to economic, demographic or other projections.

Chapter 4 builds upon the previous two chapters by examining a possible “emissions gap” in 2020 between emission levels consistent with temperature limits and expected emissions resulting from the pledges. It then goes on to explore policy options for narrowing the size of the gap.

Chapter 5 goes a step further by reporting on possible long-term temperature changes following from current pledges.

The online version of the report contains three appendices with additional information about emission pledge calculations in this report. Appendix 1 provides detail on the differences between the four pledge cases described in Chapter 3 and the uncertainties around them. Appendix 2 provides a country-by-country analysis of the pledges of the largest emitting countries. Appendix 3 compares the findings of modelling groups that have assessed country pledges.